MECHANICAL PROPERTIES OF HELA CELLS AT DIFFERENT STAGES OF CELL CYCLE BY TIME- RESOLVED ACOUSTIC MICROSCOPE. Pavel V. Zinin1 , Eike C. Weiss2, Pavlos Anastasiadis2, Robert M. Lemor2, John Allen1 1School of Ocean and Earth Science and Technology, University of Hawaii, Honolulu, USA 2Biomedical Ultrasound Research, Fraunhofer-Institute for Biomedical Technology, St. Ingbert, Germany. Mechanical factors play an important role in the regulation of cell physiology including cell division, cell motility, etc. Recently, the effects of the cell pathophysiology, in particular effect of cancer on cell viscoelasticity, have attracted the attenuation of biomedical researchers since connections between single- cell biomechanics and human cancer have been established. Despite the fact that numerous techniques are available for studying mechanical properties of biological cells such as micropipette technique, magnetic twisting cytometry, numerous laser techniques, atomic force microscopy (AFM), most the techniques allow studying either mechanical properties of only cell membrane or combination of the mechanical properties of cell membrane and cytosceleton. Scanning acoustic microscopy (SAM), particularly time-resolved acoustic microscopy, is one of the few techniques that allows studying the mechanical properties of only cell’s interior: cytosol and nucleus. Unfortunately, time-resolved acoustic microscopes that have been used so far in biology did not provide sufficient resolution to study the elasticity of a single cells. In this report, we demonstrate that the high-frequency time-resolved acoustic microscope developed at the Fraunhofer Institute for Biomedical Technology (IBMT), Germany , is capable of imaging and characterizing elastic properties of micron size structures in cell’s cytosceleton and has a theoretical resolution limit of 10 m/s when measuring sound speed of single cells. Measurements were performed on cells of the HeLa cell line derived from human cervics carcinoma. SAM measurments of sound speed of adherent HeLa cells at different states of the cell cycle have beend conducted. They yielded an average value of 1540 m/s. B-Scan images of HeLa cells at different states of the cell cycle show distinct patterns inside the cell (Fig. 1). A method for estimating sound attenuation inside HeLa cells has been presented. Such a method is critical for the determination of cell viscoelasticity. Despite the well accepted opinion that cells have no internal reflections and can be assumed to be homogeneous this has been found not to be true for HeLa cells. Acknowledgements: The financial support provided by “Alexander von Humboldt Foundation” of Germany is gratefully acknowledged. This work was supported partially by the European Framework Program 6,Project “CellProm”. References:  R. Lemor, E. C. Weiss, G. Pilarczyk, and P. V. Zinin, "Measurements of the elastic properties of the cell using high frequency time-resolved acoustic microscope," in 2003 IEEE Ultrasonic Symposium, D. E. Yuhas, Ed. New York: IEEE, 2004, pp. 881-884.
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